Pumping well fluids from wells penetrating producing formations has been done for many years. Often, heavy viscous oil must be moved to the surface. This oil can be found relatively close to the earth's surface and can contain sand and/or other solid particulate and can be difficult to pump. The presence of sand and other solids in conventional pumps can cause numerous problems, such as premature wear and/or jamming of the pump. The wear and jamming can result in high costs associated with downtime, repair, replacement, and cleanup. Additionally, the wear can create safety concerns, both for the drill crew and for the environment.
Some problems of conventional pumping systems can be attributed to the plunger and its connection to the drive rods. For example, sand can get trapped between a pump plunger and a pump barrel. As the pump reciprocates up and down in the pump barrel during operation, the sand rubs against the plunger, other pump components, and the pump barrel, causing the pump to wear excessively.
The connection between the drive rods and the pump in conventional systems can contribute to the buildup of the damaging precipitate. Specifically, the connection of the drive rod and plunger components in conventional pump systems is positioned at the top of the plunger. Sand can stack up on the top of this connection, causing the plunger to stick in the barrel when there is a power failure or power to the pump is otherwise shut off. Additionally, the geometry of the connector contributes to the problem. Oftentimes, conventional connectors are tapered outward such that any solids are funneled down and outward toward the interface between the inner wall of the pump barrel and the outer diameter of the plunger. This creates more opportunity for sand or other particulate to get between this interface and cause wear to the pump.
Conventional connectors often have a slightly smaller outer diameter than that of the plunger. For example, connector may have an outer diameter that is 1/60,000 of an inch smaller than the outer diameter of plunger. Because of such a configuration, sand tends to accumulate between the connector and the pump barrel upon reciprocation of the plunger. On further operation, the accumulated sand, coarse particulate, or other solids will find its way between the pump barrel and the plunger. As such, significant problems may occur with the pump, including stuck plungers, gaulded plungers and barrels, reduced pump efficiency, and shortened pump life.
Other problems related to sand and other precipitate in the produced fluid may arise due to the overall pump structure. Problems related to a gas build up preventing actuation of valves within the pumping system can cause the system to lock up. In conventional pumps, a hydrostatic fluid column above the pump holds a single traveling valve closed until a pressure under the traveling valve exceeds the pressure created by the hydrostatic fluid column above the traveling valve. If too much gas gets inside the pump barrel and compresses, then the traveling valve will not open and the pump is in a gas locked state.
In conventional pump systems, the pumped fluid flows through a main tubing section that is outside of an aperture of the plunger. Solids may settle out of the pumped fluid and on top of the pump, cementing or otherwise sticking the pump within the tubing. In conventional systems, when stuck, the pump cannot be retrieved by merely pulling the pump out with the drive rods. Instead the replacement of components of the pump downwell requires that the main tubing structure be removed and disassembled to access the pump, causing the pumped fluid within the main tubing structure to be spilled. This is called pulling a wet well, which can create environmental and safety problems. Improvements in handling of sand and gas within downwell pumping systems are desired.